Are you about to order a ring from an online seller? If so, you must know your ring size in order to get a ring that fits correctly. However, if you're like a lot of people and have never had your ring size officially measured -- many people buy rings by trying them on randomly, rather than by finding out the size -- you're going to have a difficult time picking the right option on the screen. If you can't get to a jeweler's to have your finger measured, here are a few home procedures that might work for you.
Plastic Ring Sizer
If you have some time before you want to order the ring, try to get a plastic ring sizer. These are often available as free gifts from some jeweler websites, or you can look in an online shop to find them. These are flat cards with several sized holes. You'd stick the finger you want to wear the ring on inside the holes until you found one that just barely fit. It should be relatively easy to remove your finger, but if you were to let go of the card, for example, it would not fall off that finger.
The downside to these is that they do take time to get. If you can hold off ordering the ring for a week or two, though, the sizer is the best alternative to actually going into a jeweler's shop for a professional fitting.
Some jewelers' websites, such as Heritage Jewelers, will have diagrams of ring sizes online, and you can use these in two ways. One is to measure the inside of a ring you already own that fits on the finger you want to wear the new ring on. Measure the diameter of the circle formed by the ring, from the inside on one side to the inside on the other side. Compare that measurement to the circles on the screen to find the matching ring size.
You can also print out the circles and place the ring on them to find the best match. You should be barely able to see the circle under the ring. Be sure that the circles include half sizes.
You might also find printable rulers that you can wrap around your finger. Use these like you would other flexible rulers, but be aware that your printer paper could make the sizing somewhat inaccurate unless you soften the paper first. You can also try using a clothing tape measure, one of the really soft and flexible ones that you find in sewing stores.
String is a last resort. The string can stretch and sag, and as you remove the string from your finger, you might lose a millimeter or two of the measurement. Use string only if you can't find other sizing instruments.
Remember to measure your finger several times throughout the week or month. That ensures that you see how your finger changes due to water retention or regular daily changes.